Form coke coated with glanz carbon and methods of production

ABSTRACT

FORM COKE, COATED WITH A FILM OF GLANZ CARBON WHICH FILLS THE MICROPORES ON THE SURFACE, IS DESCRIBED, TOGETHER WITH METHODS FOR PRDUCING THE FILM DURING THEPRODUCTION OF THE COKE.

Aprll 3, 1973 R. T. JOSEPH 3,725,018

FORM coma COATED WITH GLANZ CARBON AND METHODS OF PRODUCTION Filed April 19. 1971 r CURED l8 BRIQUETTES IN SECTION 20A I LOCK HOPPER 20 20B 38 OFF- GAS TO 36 CYCLONE SCRUBBER GAS CLEANER SECTION II T-3 COLD WATER our COAL OR CHAR TEMPERING v GAS SECTION 11 L COLD WATER |N T-6 LOCK HOPPER 32 COKED BRIQUETTES OUT INVENTOR.

ROBERT T. JOSEPH SECTION III United States Patent O FORM COKE COATED WITH GLANZ CARBON AND METHODS OF PRODUCTION Robert T. Joseph, Richboro, Pa., assignor to FMC Corporation, New York, N.Y.

Filed Apr. 19, 1971, Ser. No. 134,982 Int. Cl. C101 /00, 5/36 US. CI. 4410 R 4 Claims ABSTRACT OF THE DISCLOSURE Form coke, coated with a film of glanz carbon which fills the micropores on the surface, is described, together with methods for producing the film during the production of the coke.

BACKGROUND OF THE INVENTION conventionally, coke has been made from coking coals in by-product or beehive ovens; the coke is obtained as a mass which is discharged from the furnace in the form of lumps of irregular shape. In handling-particularly in shipping-the edges and corners of these lumps break off as fines, which cause difi-lculty in maintaining bed porosity in the blast furnace, and rapid plugging of the dust-collecting systems associated therewith. However, the fines produced are relatively coarse and are airborne with diificulty in normal handling. This tendency to produce fines is generally tested according to the American Society for Testing and Materials method AS'TM D2 94-64, called the Tumbler Test. Results are reported as the hardness factor--i.e., the weight of coke sample that is retained on the A" standard sieve after tumbling. In normal operations, any coke that degrades in handling to a size that will pass through the A" standard sieve is removed by in-transit screening as the coke moves from the supply dump to the skip car for charging to the blast furnace, so that the hardness factor measures the coke available for actual charging to the furnace.

Many attempts have been made to produce substitutes for standard coke from noncoking coals. One such material is described and claimed in Work et al. US. Pat. 3,184,293, issued May 18, 1965; it is produced by the methods described in Work et al. US. Pats. 3,140,241 and 3,140,242, issued July 7, 1964. The product made in accordance with the patents comprises briquettes made by briquetting particles of a reactive coal calcinate with oxidized coal tar pitch, curing the briquettes in an oxidizing atmosphere, and then calcining the briquettes to remove volatiles to under 3% without removing all of the hydrogen. The product is reactive with carbon dioxide, and has a high hardness factor. Tests run in an experimental blast furnace indicated that the uniform size and shape of the particles facilitated furnace operation. Moreover, the particles do not spall on burning, so that the fines problem in the blast furnace is minimized.

However, when a large-scale test in a commercial installation was made, it was found that the briquettes developed a serious fines problem substantially different from that encountered with conventional coke. After a 1,000 mile rail haul, cars of the coke, when unloaded, produced a dust cloud which surrounded the unloading point so that it was difiicult to remain close enough to the unloading area to assist in the unloading. Despite the fact that the percentage of fines was no greater than that produced from conventional coke under similar circumstances, the fines from this new form of coke were easily airborne, whereas the fines from conventional coke were not.

3,725,018 Patented Apr. 3, 1973 One suggestion for overcoming this problem of airborne dust is disclosed in Trechock et al. US. patent application Serial No. 110,608, entitled Method of Controlling Ultrafines from Reactive Form Coke, and filed Jan. 28, 1971. In accordance with that application, the reactive form coke is treated with an aqueous dispersion of a film-forming solid to deposit, on and immediately adjacent the surface, a film which contains 0.05 to 3%, and preferably 0.5 to 3%, of the film-forming solid. This treatment is indeed effective in controlling the airbornedust problem, but has a disadvantage in cost. Even 0.5% of solid is 10 pounds per short ton of coke of 5 kilos per metric ton, and preparation of the dispersion and application to form coke are costly.

OBJECT OF THE INVENTION This invention aims to provide a means for overcoming the dusting tendencies of form coke, particularly of reactive form coke, without adding to the cost of the coke.

STATEMENT OF THE INVENTION In accordance with this invention, this objective is attained by treating reactive form coke, while it is being calcined to remove volatiles therefrom, with hot gases containing sufficient hydrocarbon vapors (at least 10 volume percent of the hot gases) which are cracked in the presence of the hot form coke, to deposit thereon a thin film of glanz carbon covering the entire surface. The resultant coated reactive form coke is nondusting and nonsmutting. Since the coating occurs simultaneously with the final devolatilization, no additional process step with attendant cost is involved. In the preferred form of the invention, the hydrocarbon vapors in the hot calcining gases are obtained by introducing raw or partially charred coal in to the combustion gases used to produce the heat for calcination, thereby cooling the gases todesired operating levels and reducing the reaction between those gases and the form coke, resulting in improved quality.

The method of coating is applicable to other form cokes, and produces a coated coke with superior properties.

THE DRAWING The drawing is a schematic diagram of an apparatus in which the invention may be practiced.

DETAILED DESCRIPTION OF THE INVENTION As indicated above, this invention is designed to control a problem which seems to be unique with the carbonaceous briquettes made in accordance with US. Pats. 3,140,241 and 3,140,242. Briefly, in accordance with these patents, a reactive calcinate is made by catalyzing coal particles by heating in the presence of added oxygen (U.S. Pat. 3,140,241) or oxygen in the coal (U.S. Pat. 3,140,242) to a temperature above 250 F. and below tar-distilling temperatures, then shock-heating the particles to tar-distilling temperatures by passing them into a fluidized bed maintained at the desired tar-producing temperatures, removing substantially all of the tars in one or more carbonizing stages, and then calcining the particles at a still higher temperature to not over about 3% of volatiles, while maintaining at least 1% by weight of hydrogen in the calcinate. This reactive calcinate is then briquetted with a bituminous binder; the green briquettes are cured in the presence of oxygen at temperatures to cause oxygen-heat induced interaction between the binder and the reactive calcinate, and the cured briquettes are then calcined (coked) to produce the desired reactive product. These porous briquettes are hereinafter referred to in the specification and claims as reactive form coke.

Reactive form coke withstands the ASTM Tumbler Test better than conventional coke, but after long rail shipments and bulk handling produces the serious dusting problem hereinabove referred to. Investigation of the problem established that the dusting was due to the fact that the abraded particles had much higher proportions of ultrafines than conventional coke, and that the extreme dusting was caused by this high concentration of ultrafine particles in the to 20 micron particle size range. Microscopic investigation indicated that the cell walls of the coke were much thinner in reactive form coke than in conventional coke. There is a honeycomb of very fine pores adjacent to the surface in which the wall thickness is of the order of 1 to 5 microns, and the pores themselves are of this order of size. In addition, there are deeper pores with thicker walls. It is the thin walls which break down on abrasion to form the ultrafines.

The solution of the dusting problem is complicated by the necessity of not changing the essential characteristics of the product for blast furnace and other uses, and of course by the basic requirement of low cost.

In accordance with this invention, reactive form coke is treated, during the last stage of manufacture in which the cured briquettes are calcined to remove volatiles, to produce over the entire surface of the briquettes a uniform thin deposit of glanz carbon-Le, the silvery form of carbon which deposits when hydrocarbons are cracked. The deposit is hard and dense and, unlike the carbon of the body of the reactive form coke, Will not leave a black streak on a white streak plate. The deposit fills the very fine pores, so that there are essentially no very-thinwalled surface pores after the deposition of glanz carbon.

The deposits are produced by introducing, into the hot gases which are used for calcining the briquettes, hydrocarbon vapors in addition to those coming out of the briquettes, in sufficient concentration so that a complete film is produced over the briquette surfaces. The concentration is rather higl1at least about volume percent of the gases. Lower concentrations may produce glanz carbon, but in such low amounts that the ultrafine pores are not completely filled.

The hydrocarbon vapors may be introduced as desired, but are most preferably supplied by injecting coal or partially charred coal into the combustion gases used to provide heat for the calcination of the briquettes as they enter the kiln. This manner of supplying the hydrocarbons is useful in a variety of ways. The introduction of coal serves to temper the hot gases, and helps to reduce the flame temperatures, since the reaction of the coal with the gases is endothermic. Typically, the combustion of propane or similar gas at or near neutral to reducing conditions (necessary to prevent excessive reaction with the briquettes) produces a flame temperature of about 2800 F., whereas optimum calcination temperatures are of the order of 1500 to 1700 F. By introducing the coal into the hot flue gas, the temperature is reduced substantially, so that a lower recycle rate for the cooling gas is required.

Moreover, the coal reacts with the carbon dioxide and water vapor in the fuel combustion products, to produce carbon monoxide and hydrogen. This reduces the reactivity of the flue gas with the briquettes, thereby improving quality.

Another advantage is that additional hydrocarbon vapors are produced for collection from the off-gases of the calciner. It is believed that the improvement in yield is due only partially to the introduction of the hydrocarbons in the coal, and that additional hydrocarbon is formed in the gas stream by reaction between free radicals formed in the presence of the hot calcining coke.

Finally, the coal or char is devolatilized and, when recovered in the dust-collecting system, may be used in amounts up to 10% of the total particulate material, thus improving yields further.

While the hydrocarbon vapors in the calcining gases are preferably added to the hot untempered flue gas, they may be supplied in other more expensive ways, and still yield complete films of glanz carbon. One such method is to introduce hydrocarbons directly into the hot zone of the kiln in at least 10% concentration of the total gas volume.

In the laboratory, the desired hydrocarbon concentration can be obtained by adding raw pulverized coal to the container in which the briquettes are calcined in a laboratory muflle, so that the hydrocarbon concentration in the gas adjacent the briquettes is at the desired level; but this technique cannot be used in a plant where a moving bed of briquettes is used because the coal would fuse and plug up the kiln.

Referring to the drawing, a vertical kiln 10 is provided, consisting of a feeding section 12, a heating section 14, and a cooling section 16.

Cured briquettes are charged into the feeding section 12 by means of a belt 18; they are fed b gravity into the heating section 14 in units by means of lock hopper 20, which has slides 20A and 20B which operate alternately, so that the amount of material in the lock hopper 20 is fed into the heating section 14 in units.

The heating section 14 is heated by combustion gases from a flame 22 in which propane or other gas is burned. The flames discharge into a vertical chamber 24, at the bottom of which coal or partially charred coal is introduced through line 26, together with tempering gases. The mixture of coal, flame gas and tempering gases goes through an elongated mixing and reaction chamber 28, and discharges into the heating section 14, near its bottom, to calcine the briquettes. The heated sections 14, 24 and 28 are all carefully lined with refractory 30 and covered with insulation 31 in customary manner.

The briquettes feed by gravity from the heating section 14 into the cooling section 16, which is water-jacketed. A removal lock hopper 32, with gates 32A and 32B, is synchronized with lock hopper 20 to ensure that material added and removed is in balance; this lock hopper 32 discharges onto a belt 34, which moves the finished calcined and cooled briquettes to storage or shipment.

The gases in the calcining section go through a cyclone system 36, which may be a single cyclone or a series, to remove entrained solids; the off-gases pass through line 38 to a scrubber where tars are removed. These tars generally contain about 6 to 10% of char carried over from the cyclone system. Both the solids and tars are useful as part of the charge to the briquetting process.

Thermocouples are provided as indicated at T1 through T6, to enable proper temperature control of the process. T1 measures flame temperature; T2 measures inlet gas temperature to the calciner; T3 and T4 measure kiln temperatures in the center and at the top; T5 measures offgas temperature; and T6 measures cooled-briquette temperatures.

Typically, T1 is about 2800 F.; T2 about 1600 to 1700 F.; T3 about 1500 to 1600 F.; T4 about 900 F.; T5 about 500 to 600 F. However, the temperatures may vary within any desired limits needed for calcination of the particular form coke being heated.

As indicated above, the invention is most useful with reactive form coke, the glanz carbon-coated reactive form coke being markedly superior to the uncoated product in abrasion resistance and other handling properties, while being rapidly reactive.

The process can be applied to other coke briquettes made by briquetting nonreactive carbonaceous particles with bituminous binders, and then coking at high temperatures, with or without preliminary curing in the presence of oxygen. Glanz carbon coatings are produced thereon which help retard abrasion due to mechanical handling. The coatings do not, however, cure the spalling problem on burning, which is a major difiiculty with such other form cokes.

EXAMPLES OF THE INVENTION The following specific examples of the invention are given by way of illustration only.

EXAMPLE 1 (LABORATORY TEST) Cured briquettes, made from Illinois No. 6 seam coal according to the mehods described in Work et a1. U.S. Pat. 3,140,241, issued July 7, 1964, through the curing cycle, were used in this test. Two identical charges of 40 grams of 1%" X 1" x "/s pillow briquettes (to the nearest whole briquette) were put into 250 milliliter stainless steel beakers, and the beakers were placed in a mufile furnace heated to 1750 F. for a minute coking period. Into one of the beakers, there was added 1 gram of Illinois No. 6 seam raw coal; the other was not so treated. After coking and cooling, the briquettes were compared. Those coked without added coal being present were black and streaky, and had the typical fine surface pores of the prior art. The briquettes coked in the presence of the coal had a uniform film of glanz carbon over the surface, which filled the 5 micron surface pores; the briquettes did not streak black.

EXAMPLE 2 1 /2" x 1 /2" x 1" briquettes, made in accordance with Work et a1. U.S. Pat. 3,140,241 from Illinois No. 6 seam coal but processed only through curing, were charged into the lock hopper of the apparatus shown in the drawing, and calcined at about 1800 F. (T2 on the drawing) while feeding through the apparatus at the rate of pounds per minute, until about 600 pounds of cured briquettes were processed. Raw Elkol-Adaville seam coal from Kemmerer, Wyo. (a subbituminous B coal), ground to 16 mesh, was introduced at point 26, at the rate of 0.2 pound per minute; it passed through the briquettes in the heating section 14 and was recovered in the cyclone 36 as a powder with a volatile content of only 4%. The cooled briquettes discharged at the bottom of the coking kiln had a uniform deposit of glanz carbon; under a microscope, all the surface pores of 5 microns or less were filled, and the glanz carbon film coated the larger pores. As compared with similar coked briquettes made from the same batch of cured briquettes without the addition of the coal, the dust passing 325 mesh produced in a similar test declined from 0.58 to 0.2%, with an even greater decline in the amount of very fine (-5 micron) dust.

EXAMPLE 3 Example 2 was repeated, using rather poor quality cured briquettes made from the Elkol-Adaville coal used raw in Example 2. Its dust index was rather high to start with (0.75% of -325 mesh), and it dusted badly. However, after being coked in the presence of tar vapors derived from raw coal as described in Example 2, the amount of 325 mesh dust was down to 0.4% and the ultrafines were low enough so that the product did not produce an airborne dust.

Obviously, examples can be multiplied indefinitely without departing from the scope of the invention as defined in the claims.

I claim:

1. Form coke briquettes carrying on their surfaces a film of hard, dense silvery glanz carbon which fills the -5 micron crevices on the surfaces of the briquettes and coats the remainder of the surfaces, the briquettes being characterized by being more resistant to abrasion and dusting than the uncoated briquettes.

2. The briquettes of claim 1, in which the form coke is reactive form coke.

3. The method of treating form coke briquettes which comprises coking the briquettes in the presence of a gas containing at least 10 volume percent of hydrocarbon vapor to crack the hydrocarbon vapors in the presence of the coke briquettes and deposit a film of hard, dense silvery glanz carbon which fills the very fine crevices and coats the surface, whereby the coated briquette is more resistant to abrasion and dusting than the uncoated briquette.

4. The method of claim 3 in which the form coke is reactive form coke, and the briquettes are cured in the presence of oxygen before coking.

References Cited UNITED STATES PATENTS 3,184,293 5/1965 Work et a1. 44-10 R 1,941,462 1/1934 Bunce 2016 2,600,430 6/1952 Riblett 20854 2,789,084 4/ 1957 Schutte 20854 CARL F. DEES, Primary Examiner U.S. Cl. X.R. 44-14 

